The molecular details of virus transmission by insect vectors are being investigated by examining the gene expression and genome structure of transmissible and non-transmissible isolates of wound tumor virus (WTV). The interaction of WTV with its vector is highly specific resulting in a noncytopathic persistent infection in which viral gene expression is finely regulated. Using specific probes (cloned cDNA and monoclonal antibodies) the nature of this regulation is being studied primarily by examining the interactions of viral mRNA with host and viral specific factors. Information gained from these investigations is potentially useful for designing strategies for regulating the expression of foreign genetic information in eukaryotic cells. Maintenance of WTV exclusively in the host results in loss of transmissibility. The basis of this phenomenon is being investigated by comparing the genome structure of transmissible and nontransmissible WTV isolates and by conducting a series of mixed infection experiments designed to determine whether loss of transmissibility is a result of lesions in specific viral genome segments or a consequence of the generation of interfering virus particles. By investigating the loss of transmissibility, it may be possible to identify those elements required for efficient transmission. The molecular details of WTV transmission will also be studied by developing conditions for the independent expression of WTV genome segments in cultured vector cells. Using this approach it may be possible to identify those WTV gene products intimately involved in regulation of viral gene expression or to identify the precise nucleotide sequences required for efficient transcription, replication or packaging of the double-stranded genome RNA. The ability to control insect vectors and the diseases they transmit is currently accomplished at considerable expense to man and his environment. Research aimed at gaining a clear understanding of the molecular details of virus-vector-host interactions represents a fundamental step toward the development of safe, economical and effective means to control or eliminate insect transmitted diseases. It is anticipated that information gained from the study of the WTV-vector-host system will be useful for the eventual manipulation of similar but less well characterized systems in order to prevent transmission of disease agents.